Did you also try not including it too? (I assume so). It’s a hard bug to figure out. There’s a few discussions on debugging it on the forum, I’ll see what I can dig up but basically another way of doing it is finding the maximum pixel value in your mask, add 1 to it and that tells you the number of classes as well.
This is common when we don’t know how the data was prepared beforehand, and it’s an issue that you don’t realize until you’ve started working with the data
@mgloria try incorporating some of the advice here: CUDA error: device-side assert triggered